Polymer flow index modifier

ABSTRACT

Embodiments of the present disclosure are directed towards method for modifying a polymer flow index. As an example, a method for modifying a polymer flow index can include providing monomers to a polymerization reactor, providing a chromium catalyst to the polymerization reactor, and providing an active amount of a flow index modifier to the polymerization reactor, wherein the flow index modifier is selected from carbon dioxide, carbon monoxide, 2,4-hexadiene, and combinations thereof.

This application is a Divisional of application Ser. No. 16/094,555filed on Oct. 18, 2018 and published as U.S. Publication No.2019-0119416 A1 on Apr. 25, 2019, which is a National Stage Applicationunder 35 U.S.C. § 371 of International Application NumberPCT/US2017/027872, filed Apr. 17, 2017 and published as WO 2017/184483on Oct. 26, 2017, which claims the benefit to U.S. ProvisionalApplication 62/325,175, filed Apr. 20, 2016, the entire contents ofwhich are incorporated herein by reference in its entirety.

FIELD OF DISCLOSURE

Embodiments of the present disclosure are directed towards modifying apolymer flow index, more specifically, embodiments are directed towardsmodifying a polymer flow index by utilizing a flow index modifier with achromium catalyst.

BACKGROUND

Polymers may be utilized for a number of products including films andpipes, among other. Polymers can be formed by reacting one or more typesof monomer in a polymerization reaction. There is continued focus in theindustry on developing new and improved materials and/or methods thatmay be utilized to form polymers having one or more desirableproperties.

SUMMARY

The present disclosure provides methods for modifying a polymer flowindex, including: providing ethylene monomers to a polymerizationreactor; providing a chromium catalyst to the polymerization reactor;and providing an active amount of a flow index modifier to thepolymerization reactor.

The flow index modifier can be selected from carbon dioxide, carbonmonoxide, 2,4-hexadiene, and combinations thereof.

The present disclosure provides that carbon dioxide may be utilized from0.50 parts per million to 50.00 parts per million based upon theethylene monomers.

The present disclosure provides that carbon monoxide may be utilizedfrom 0.010 parts per million to 2.00 parts per million based upon theethylene monomers.

The present disclosure provides that 2,4-hexadiene may be utilized from0.05 parts per million to 5.00 parts per million based upon the ethylenemonomers.

The above summary of the present disclosure is not intended to describeeach disclosed embodiment or every implementation of the presentdisclosure. The description that follows more particularly exemplifiesillustrative embodiments. In several places throughout the application,guidance is provided through lists of examples, which examples can beused in various combinations. In each instance, the recited list servesonly as a representative group and should not be interpreted as anexclusive list.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a portion of a polymerization system inaccordance with one or more embodiments of the present disclosure.

FIG. 2 illustrates polymer flow index and catalyst productivity forutilizing an active amount of flow index modifier with a chromiumcatalyst.

FIG. 3 illustrates polymer density and fluidized bulk density forutilizing an active amount of flow index modifier with a chromiumcatalyst.

FIG. 4 illustrates polymer flow index and catalyst productivity forutilizing an active amount of flow index modifier with a chromiumcatalyst.

FIG. 5 illustrates polymer density and fluidized bulk density forutilizing an active amount of flow index modifier with a chromiumcatalyst.

FIG. 6 illustrates polymer flow index and catalyst productivity forutilizing an active amount of flow index modifier with a chromiumcatalyst.

FIG. 7 illustrates polymer density and fluidized bulk density forutilizing an active amount of flow index modifier with a chromiumcatalyst.

DETAILED DESCRIPTION

Methods modifying a polymer flow index and polymers formed therefrom aredescribed herein. As described herein, polymer flow index is a propertythat may affect the suitability of a polymer for particularapplications. Polymer flow index, which may also be referred to as meltflow index, is a measure of melt flow of a polymer, e.g., athermoplastic polymer. Polymer flow index can be utilized as an indirectmeasure of molecular weight. For instance, a greater polymer flow indexassociated with a particular polymer may indicate that the particularpolymer has lower average molecular weight that another polymerassociated with a relatively lesser polymer flow index. Because somepolymers having a particular polymer flow index may not suitable for anumber of particular applications, it may be desirable to modify thepolymer flow index so that the polymers are suitable for number ofparticular applications, for example.

Embodiments of the present disclosure provide methods for modifying apolymer flow index. A method for modifying a polymer flow index caninclude providing ethylene monomers, e.g., an ethylene monomer feed, toa polymerization reactor; providing a chromium catalyst to thepolymerization reactor; and providing a flow index modifier to thepolymerization reactor, wherein the flow index modifier is selected fromcarbon dioxide, carbon monoxide, 2,4-hexadiene, and combinationsthereof, for instance.

Surprisingly, it has been found that a polymer flow index may bymodified, e.g., decreased or increased, by utilizing a flow indexmodifier with a chromium catalyst as discussed further herein.Embodiments of the present disclosure provide that the flow indexmodifier is selected from carbon dioxide, carbon monoxide,2,4-hexadiene, and combinations thereof.

As mentioned, methods for modifying a polymer flow index and polymersformed therefrom are described herein. As used herein a “polymer” hastwo or more of the same or different polymer units derived from one ormore different monomers, e.g., homopolymers, copolymers, terpolymers,etc. A “homopolymer” is a polymer having polymer units that are thesame. A “copolymer” is a polymer having two or more polymer units thatare different from each other. A “terpolymer” is a polymer having threepolymer units that are different from each other. “Different” inreference to polymer units indicates that the polymer units differ fromeach other by at least one atom or are different isomerically.Accordingly, the definition of copolymer, as used herein, includesterpolymers and the like.

Embodiments of the present disclosure provide that the polymer can be apolyolefin. As used herein an “olefin,” which may be referred to as an“alkene,” refers to a linear, branched, or cyclic compound includingcarbon and hydrogen and having at least one double bond. As used herein,when a polymer or copolymer is referred to as comprising, e.g., beingformed from, an olefin, the olefin present in such polymer or copolymeris the polymerized form of the olefin. For example, when a copolymer issaid to have an ethylene content of 75 wt % to 85 wt %, it is understoodthat the polymer unit in the copolymer is derived from ethylene in thepolymerization reaction and the derived units are present at 75 wt % to85 wt %, based upon the total weight of the polymer. A higher α-olefinrefers to an α-olefin having 4 or more carbon atoms.

Polyolefins include polymers made from olefin monomers such as ethylene,i.e., polyethylene, and linear or branched higher alpha-olefin monomerscontaining 3 to about 20 carbon atoms. Examples of higher alpha-olefinmonomers include, but are not limited to, propylene, 1-butene,1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and3,5,5-trimethyl-l-hexene. Examples of polyolefins include ethylene-basedpolymers, having at least 50 wt % ethylene, including ethylene-1-butene,ethylene-1-hexene, and ethylene-1-octene copolymers, among others. Otherolefins that may be utilized include ethylenically unsaturated monomers,diolefins having 4 to 18 carbon atoms, conjugated or nonconjugateddienes, polyenes, vinyl monomers and cyclic olefins, for example.Examples of the monomers may include, but are not limited to,norbornene, norbornadiene, isobutylene, isoprene, vinylbenzocyclobutane,styrenes, alkyl substituted styrene, ethylidene norbornene,dicyclopentadiene and cyclopentene. In a number of embodiments, acopolymer of ethylene can be produced, where with ethylene, a comonomerhaving at least one alpha-olefin having from 4 to 15 carbon atoms,preferably from 4 to 12 carbon atoms, and most preferably from 4 to 8carbon atoms, is polymerized, e.g., in a gas phase process. In anotherembodiment, ethylene and/or propylene can be polymerized with at leasttwo different comonomers, optionally one of which may be a diene, toform a terpolymer.

Embodiments of the present disclosure provide that the polymers can havea density of from 0.920 to 0.970 g/cm³. For example, the polymers canhave a density of ≥0.920 g/cm³, ≥0.930 g/cc, ≥0.935 g/cm³, ≥0.940 g/cm³,or ≥0.945 g/cm³, and ≤0.970 g/cm³, ≤0.960 g/cm³, ≤0.950 g/cm³, ≤0.935g/cm³, ≤0.930 g/cm³, or ≤0.925 g/cm³, or any combination of any high orlow value recited herein. For instance, the polymers can have a densityof 0.925 to 0.950 g/cm³, 0.930 to 0.940 g/cm³, 0.935 to 0.945 g/cm³, and0.935 to 0.950 g/cm³, among others.

Generally, a relatively greater co-monomer content can result in arelatively lower density. Polyethylene copolymers herein can have aco-monomer content of ≥0 to 15 wt % based on a total weight of thepolyethylene copolymer, e.g., 1.0 to 12.0 wt %, 2.0 to 10.0 wt %, 2.0 to8.0 wt %, 2.0 to 7.0 wt %, 2.0 to 6.0 wt %, for example, where thepolyethylene copolymers comprise co-monomer units derived from 1-buteneand/or 1-hexene.

Embodiments of the present disclosure provide that the polymers can havea weight-averaged molecular weight (Mw)≥about 100,000 g/mol, ≥about150,000 g/mol≥about 200,000 g/mol, ≥about 300,000 g/mol, ≥about 400,000g/mol, ≥about 500,000 g/mol, ≥about 750,000 g/mol, or ≥about 1,000,000g/mol. Additionally or alternatively, the Mw may be ≤about 1,000,000g/mol, ≤about 750,000 g/mol, ≤about 1,000,000 g/mol, ≤about 500,000g/mol, ≤about 400,000 g/mol, ≤about 300,000 g/mol, ≤about 200,000 g/mol,or ≤about 150,000 g/mol, or combinations of high or low values thatprovide ranges, as recited herein.

Embodiments of the present disclosure provide that the polymers can havea polymer flow index, e.g., a modified polymer flow index, of ≥about0.01 g/10 min, ≥about 0.02 g/10 min, ≥about 0.10 g/10 min, ≥about 0.50g/10 min, ≥about 0.75 g/10 min, ≥about 1.0 g/10 min, ≥about 2.0 g/10min, ≥about 5.0 g/10 min, ≥about 10.0 g/10 min., or ≥about 25.0 g/10min. Additionally or alternatively, the polymer flow index may be ≤about50.0 g/10 min, e.g., ≤about 25.0 g/10 min, ≤about 10.0 g/10 min, ≤about5.0 g/10 min, ≤about 2.0 g/10 min, ≤about 1.0 g/10 min, or ≤about 0.50g/10 min. The polymer flow index may be in a range that includes acombination of any high and low values disclosed herein. For example,the polymers can have a polymer flow index in a range of about 0.01 toabout 50.0 g/10 min, about 0.01 to about 25.0 g/10 min, about 0.01 toabout 10.0 g/10 min, about 0.01 to about 5.0 g/10 min, about 0.01 toabout 2.0 g/10 min, among others.

As mentioned, embodiments of the present disclosure provide methods formodifying a polymer flow index by utilizing a flow index modifier. Theflow index modifier can be utilized to modify, e.g., change, a polymerflow index of polymer. For instance, a polymerization process can beutilized to form a polymer having a first polymer flow index; a flowindex modifier may subsequently be added to the polymerization processto modify the polymer flow index to a second polymer flow index that isdifferent than the first polymer flow index. Additionally oralternatively, a polymerization process, which includes a flow indexmodifier, can be utilized to form a polymer having a first polymer flowindex, where the first polymer flow index is different than a secondpolymer flow index that would be realized by forming the polymer via thepolymerization process without utilizing the flow index modifier.

Embodiments of the present disclosure provide that the flow indexmodifier is selected from carbon dioxide, carbon monoxide,2,4-hexadiene, and combinations thereof.

A number of embodiments of the present disclosure provide that carbondioxide may be utilized in an active amount as the flow index modifier.The carbon dioxide, i.e., the active amount, can be from 0.50 parts permillion to 50.00 parts per million based upon ethylene monomers utilizedto form the polymer, e.g., the ethylene monomer feed. All individualvalues and subranges from 0.50 parts per million to 50.00 parts permillion are included; for example, the carbon dioxide can be from alower limit of 0.50 parts per million, 1.00 parts per million, 2.50parts per million, 5.00 parts per million, 10.00 parts per million, or15.00 parts per million based upon the ethylene monomers to an upperlimit of 50.00 parts per million, 45.00 parts per million, 40.00 partsper million, 37.50 parts per million, 35.00 parts per million, or 30.00parts per million based upon the ethylene monomers. For one or moreembodiments, the carbon dioxide can be about 25 parts per million basedupon the ethylene monomer feed. As used herein, “parts per million”indicates parts per million volume (ppmv), unless indicated otherwise.

Utilizing a flow index modifier comprising carbon dioxide can provide,e.g., form, a polymer having a polymer flow index, e.g., a modifiedpolymer flow index, which is reduced as compared to a second polymerhaving a different polymer flow index, where the second polymer isformed by the same polymerization process, but without utilizing anactive amount of the flow index modifier. For instance, utilizing a flowindex modifier comprising carbon dioxide can provide a polymer having apolymer flow index, e.g., the modified polymer flow index, that isreduced from about 5% to about 50% as compared to a second polymerhaving a different polymer flow index, where the second polymer isformed by the same polymerization process, but without utilizing anactive amount of the flow index modifier. All individual values andsubranges from about 5% to about 50% are included; for example,utilizing a flow index modifier comprising carbon dioxide can provide apolymer having a polymer flow index that is reduced from a lower limitof about 5%, about 7%, about 10%, or about 15% to an upper limit ofabout 50%, about 45%, about 40%, or about 35%, as compared to a secondpolymer having a different polymer flow index, where the second polymeris formed by the same polymerization process, but without utilizing anactive amount of the flow index modifier. For one or more embodiments,utilizing a flow index modifier comprising carbon dioxide can provide apolymer having a polymer flow index that is reduced about 30%, ascompared to a second polymer having a different polymer flow index,where the second polymer is formed by the same polymerization process,but without utilizing an active amount of the flow index modifier.

Utilizing a flow index modifier comprising carbon dioxide can provide apolymer having a density that is reduced as compared to a second polymerhaving a different density, where the second polymer is formed by thesame polymerization process, but without utilizing an active amount ofthe flow index modifier. For instance, utilizing a flow index modifiercomprising carbon dioxide can provide a polymer having a density that isreduced by about 0.0002 g/cm³ to about 0.0040 g/cm³ as compared to asecond polymer having a different density, where the second polymer isformed by the same polymerization process, but without utilizing anactive amount of the flow index modifier. All individual values andsubranges from about 0.0002 g/cm³ to about 0.0040 g/cm³ are included;for example, utilizing a flow index modifier comprising carbon dioxidecan provide a polymer having a density that is reduced by a lower limitof about 0.0002 g/cm³, 0.00025 g/cm³, or 0.00028 g/cm³ to an upper limitof about 0.0040 g/cm³, 0.0035 g/cm³, or 0.0032 g/cm³.

Utilizing a flow index modifier comprising carbon dioxide can provide apolymer having a fluidized bulk density that is increased as compared toa second polymer having a different fluidized bulk density, where thesecond polymer is formed by the same polymerization process, but withoututilizing an active amount of the flow index modifier. For instance,utilizing a flow index modifier comprising carbon dioxide can provide apolymer having a fluidized bulk density that is increased from about0.5% to about 5.5% as compared to a second polymer having a differentfluidized bulk density, where the second polymer is formed by the samepolymerization process, but without utilizing an active amount of theflow index modifier. All individual values and subranges from about 0.5%to about 5.5% are included; for example, utilizing a flow index modifiercomprising carbon dioxide can provide a polymer having a fluidized bulkdensity that is increased from a lower limit of about 0.5%, about 0.7%,about 1.0%, or about 1.5% to an upper limit of about 5.5%, about 5.0%,about 4.7%, or about 4.5%, as compared to a second polymer having adifferent fluidized bulk density, where the second polymer is formed bythe same polymerization process, but without utilizing an active amountof the flow index modifier.

A number of embodiments of the present disclosure provide that carbonmonoxide may be utilized in an active amount as the flow index modifier.The carbon monoxide, i.e., the active amount, can be from 0.010 partsper million to 2.000 parts per million based upon ethylene monomersutilized to form the polymer, e.g., the ethylene monomer feed. Allindividual values and subranges from 0.010 parts per million to 2.000parts per million are included; for example, the carbon monoxide canfrom a lower limit of 0.010 parts per million, 0.015 parts per million,0.0.020 parts per million, 0.025 parts per million, 0.030 parts permillion, or 0.0.050 parts per million based upon the ethylene monomersto an upper limit of 2.00 parts per million, 1.750 parts per million,1.500parts per million, 1.250 parts per million, 1.150 parts permillion, or 1.000 parts per million based upon the ethylene monomers.For one or more embodiments, the carbon monoxide can be about 0.20 partsper million based upon the ethylene monomer feed. For one or moreembodiments, the carbon monoxide can be about 0.50 parts per millionbased upon the ethylene monomer feed.

Utilizing a flow index modifier comprising carbon monoxide can provide apolymer having a polymer flow index, e.g., a modified polymer flowindex, which is reduced as compared to a second polymer having adifferent polymer flow index, where the second polymer is formed by thesame polymerization process, but without utilizing an active amount ofthe flow index modifier. For instance, utilizing a flow index modifiercomprising carbon monoxide can provide a polymer having a polymer flowindex, e.g., the modified polymer flow index, that is reduced from about5% to about 50 as compared to a second polymer having a differentpolymer flow index, where the second polymer is formed by the samepolymerization process, but without utilizing an active amount of theflow index modifier. All individual values and subranges from about 5%to about 50% are included; for example, utilizing a flow index modifiercomprising carbon monoxide can provide a polymer having a polymer flowindex that is reduced from a lower limit of about 5%, about 7%, about10%, or about 15% to an upper limit of about 50%, about 45%, about 40%,or about 35%, as compared to a second polymer having a different polymerflow index, where the second polymer is formed by the samepolymerization process, but without utilizing an active amount of theflow index modifier. For one or more embodiments, utilizing a flow indexmodifier comprising carbon monoxide can provide a polymer having apolymer flow index that is reduced about 30%, as compared to a secondpolymer having a different polymer flow index, where the second polymeris formed by the same polymerization process, but without utilizing anactive amount of the flow index modifier.

Utilizing a flow index modifier comprising carbon monoxide can provide apolymer having a density that is reduced as compared to a second polymerhaving a different density, where the second polymer is formed by thesame polymerization process, but without utilizing an active amount ofthe flow index modifier. For instance, utilizing a flow index modifiercomprising carbon monoxide can provide a polymer having a density thatis reduced by about 0.0002 g/cm³ to about 0.0040 cm³ as compared to asecond polymer having a different density, where the second polymer isformed by the same polymerization process, but without utilizing anactive amount of the flow index modifier. All individual values andsubranges from about 0.0002 g/cm³ to about 0.0040 g/cm³ are included;for example, utilizing a flow index modifier comprising carbon monoxidecan provide a polymer having a density that is reduced by a lower limitof about 0.0002 g/cm³, 0.00022 g/cm³, or 0.00024 g/cm³ to an upper limitof about 0.0040 g/cm³, 0.0035 g/cm³, or 0.0032 g/cm³.

Utilizing a flow index modifier comprising carbon monoxide can provide apolymer having a fluidized bulk density that is increased as compared toa second polymer having a different fluidized bulk density, where thesecond polymer is formed by the same polymerization process, but withoututilizing an active amount of the flow index modifier. For instance,utilizing a flow index modifier comprising carbon monoxide can provide apolymer having a fluidized bulk density that is increased from about2.0% to about 12.5% as compared to a second polymer having a differentfluidized bulk density, where the second polymer is formed by the samepolymerization process, but without utilizing an active amount of theflow index modifier. All individual values and subranges from about 2.0%to about 12.5% are included; for example, utilizing a flow indexmodifier comprising carbon monoxide can provide a polymer having afluidized bulk density that is increased from a lower limit of about2.0%, about 2.5%, about 3.0%, or about 3.5% to an upper limit of about12.5%, about 12.0%, about 11.5%, or about 11.0%, as compared to a secondpolymer having a different fluidized bulk density, where the secondpolymer is formed by the same polymerization process, but withoututilizing an active amount of the flow index modifier.

A number of embodiments of the present disclosure provide that2,4-hexadiene may be utilized in an active amount as the flow indexmodifier. The 2,4-hexadiene, i.e., the active amount, can be from 0.05parts per million to 5.00 parts per million based upon ethylene monomersutilized to form the polymer, e.g., the ethylene monomer feed. Allindividual values and subranges from 0.05 parts per million to 5.00parts per million are included; for example, the 2,4-hexadiene can froma lower limit of 0.05 parts per million, 0.10 parts per million, or 0.50parts per million based upon the ethylene monomers to an upper limit of5.00 parts per million, 4.50 parts per million, or 4.00 parts permillion based upon the ethylene monomers. For one or more embodiments,the 2,4-hexadiene can be about 0.70 parts per million based upon theethylene monomer feed. For one or more embodiments, the 2,4-hexadienecan be about 2.78 parts per million based upon the ethylene monomerfeed.

Utilizing a flow index modifier comprising 2,4-hexadiene can provide apolymer having a polymer flow index, e.g., a modified polymer flowindex, which is increased as compared to a second polymer having adifferent polymer flow index, where the second polymer is formed by thesame polymerization process, but without utilizing an active amount ofthe flow index modifier. For instance, utilizing a flow index modifiercomprising 2,4-hexadiene can provide a polymer having a polymer flowindex, e.g., the modified polymer flow index, that is increased fromabout 10% to about 75% as compared to a second polymer having adifferent polymer flow index, where the second polymer is formed by thesame polymerization process, but without utilizing an active amount ofthe flow index modifier. All individual values and subranges from about10% to about 75% are included; for example, utilizing a flow indexmodifier comprising 2,4-hexadiene can provide a polymer having a polymerflow index that is increased from a lower limit of about 10%, about 12%,or about 15 to an upper limit of about 75%, about 73%, or about 70%, ascompared to a second polymer having a different polymer flow index,where the second polymer is formed by the same polymerization process,but without utilizing an active amount of the flow index modifier. Forone or more embodiments, utilizing a flow index modifier comprising2,4-hexadiene can provide a polymer having a polymer flow index that isincreased about 50%, as compared to a second polymer having a differentpolymer flow index, where the second polymer is formed by the samepolymerization process, but without utilizing an active amount of theflow index modifier.

Utilizing a flow index modifier comprising 2,4-hexadiene can provide apolymer having a density that is increased as compared to a secondpolymer having a different density, where the second polymer is formedby the same polymerization process, but without utilizing an activeamount of the flow index modifier. For instance, utilizing a flow indexmodifier comprising 2,4-hexadiene can provide a polymer having a densitythat is increased from about 0.0005 g/cm³ to about 0.0030 g/cm³ ascompared to a second polymer having a different density, where thesecond polymer is formed by the same polymerization process, but withoututilizing an active amount of the flow index modifier. All individualvalues and subranges from about 0.0005 g/cm³ to about 0.0030 g/cm³ areincluded; for example, utilizing a flow index modifier comprising2,4-hexadiene can provide a polymer having a density that is increasedfrom a lower limit of about 0.0005 g/cm³, 0.0007 g/cm³, or 0.0010 g/cm³to an upper limit of about 0.0030 g/cm³, 0.0027 g/cm³, or 0.0025 g/cm³.

Utilizing a flow index modifier comprising 2,4-hexadiene can provide apolymer having a fluidized bulk density that is decreased as compared toa second polymer having a different fluidized bulk density, where thesecond polymer is formed by the same polymerization process, but withoututilizing an active amount of the flow index modifier. For instance,utilizing a flow index modifier comprising 2,4-hexadiene can provide apolymer having a fluidized bulk density that is decreased from about5.0% to about 15.0% as compared to a second polymer having a differentfluidized bulk density, where the second polymer is formed by the samepolymerization process, but without utilizing an active amount of theflow index modifier. All individual values and subranges from about 5.0%to about 15.0% are included; for example, utilizing a flow indexmodifier comprising 2,4-hexadiene can provide a polymer having afluidized bulk density that decreased from a lower limit of about 5.0%,about 6.0%, or about 7.0% to an upper limit of about 15.0%, about 14.0%,or about 13.0%, as compared to a second polymer having a differentfluidized bulk density, where the second polymer is formed by the samepolymerization process, but without utilizing an active amount of theflow index modifier.

FIG. 2 illustrates polymer flow index and catalyst productivity forutilizing an active amount of flow index modifier, i.e., carbon dioxide,with a chromium catalyst. FIG. 3 illustrates polymer density andfluidized bulk density for utilizing an active amount of flow indexmodifier, i.e., carbon dioxide, with a chromium catalyst. FIG. 4illustrates polymer flow index and catalyst productivity for utilizingan active amount of flow index modifier, i.e., carbon monoxide, with achromium catalyst. FIG. 5 illustrates polymer density and fluidized bulkdensity for utilizing an active amount of flow index modifier, i.e.,carbon monoxide, with a chromium catalyst. FIG. 7 illustrates polymerflow index and catalyst productivity for utilizing an active amount offlow index modifier, i.e., 2,4-hexadiene, with a chromium catalyst. FIG.7 illustrates polymer density and fluidized bulk density for utilizingan active amount of flow index modifier, i.e., 2,4-hexadiene, with achromium catalyst. FIG. 6 and FIG. 7 illustrate that the polymer flowindex and polymer density may pass through maximum values withincreasing levels of 2,4-hexadiene; fluidized bulk density may passthrough a minimum value; and catalyst productivity may decrease withincreasing 2,4-hexadiene levels. As used herein, “maximum value” and“minimum value” each refer to respective extreme values associated witha respective trend line, e.g., the trend lines included in FIGS. 6 and 7, where the slopes of the respective trend lines are zero. FIG. 6 andFIG. 7 each include a respective dotted and straight line from they-axis (i.e., where no carbon dioxide, carbon monoxide, or 2,4-hexadienewas utilized for the polymerization) to the greater concentration of2,4-hexadiene utilized in the Examples, to illustrate changes ascompared to the observed maxima and minima responses, which the lines donot pass directly through.

A number of embodiments of the present disclosure provide that one ormore catalysts may be utilized in forming the polymers. The catalyst,which includes and may be referred to as a catalyst composition, may bea chromium catalyst. As used herein “chromium catalyst” refers to acatalyst that includes chromium. The catalyst may include a reducingagent. For a number of embodiments of the present disclosure, thechromium catalyst is a chromium oxide catalyst reduced with metal alkyl.In other words, a reduced chromium oxide catalyst may be utilized toform the polymer having the modified polymer flow index, as describedherein. For initialization of the polymerization, e.g., for a pilotplant polymerization, a silyl chromate catalyst reduced with metal alkylmay be employed before transitioning to the reduced chromium oxidecatalyst. The silyl chromate catalyst may be referred to as a startupcatalyst. Alternatively, the reduced chromium oxide catalyst may be usedto initiate polymerization with similar performance as the silylchromate catalyst.

Chromium compounds may be used to prepare chromium oxide catalysts.Chromium compounds include CrO₃, as well as other compounds that areconvertible to CrO₃, e.g., under activation conditions. Examples ofcompounds that are convertible to CrO₃ include chromic acetyl acetonate,chromic halide, chromic nitrate, chromic acetate, chromic sulfate,ammonium chromate, ammonium dichromate, or other soluble, chromiumcontaining salts. Other examples of compounds that are convertible toCrO₃ include those discussed in U.S. Pat. Nos. 2,825,721, 3,023,203,3,622,251, and 4,011,382, for instance. In a number of embodiments,chromic acetate may be utilized.

Silyl chromate compounds may be used to prepare the silyl chromatecatalysts. Silyl chromate compounds include bis-triethylsilyl chromate,bis-tributylsilyl chromate, bis-triisopentylsilyl chromate,bis-tri-2-ethylhexylsilyl chromate, bis-tridecylsilyl chromate,bis-tri(tetradecyl)silyl chromate, bis-tribenzylsilyl chromate,bis-triphenylethylsilyl chromate, bis-triphenylsilyl chromate,bis-tritolylsilyl chromate, bis-trixylylsilyl chromate,bis-trinaphthylsilyl chromate, bis-triethylphenylsilyl chromate,bis-trimethylnaphthylsilyl chromate, polydiphenylsilyl chromate, andpolydiethylsilyl chromate. Examples of such catalysts are discussed, forexample, in U.S. Pat. Nos. 3,324,101, 3,704,287, and 4,100,105, amongothers. In some embodiments, bis-triphenylsilyl chromate,bis-tritolylsilyl chromate, bis-trixylylsilyl chromate, andbis-trinaphthylsilyl chromate may be utilized. In other embodiments,bis-triphenylsilyl chromate may be utilized.

The silyl chromate compounds may be deposited onto conventional catalystsupports or bases, for example, inorganic oxide materials. The chromiumcompound used to produce a chromium oxide catalyst may be deposited ontoconventional catalyst supports. The term “support,” as used herein,refers to any support material, a porous support material in oneexemplary embodiment, including inorganic or organic support materials.The supports may be inorganic oxides that include Group 2, 3, 4, 5, 13and 14 oxides, and more particularly, inorganic oxides of Group 13 and14 atoms. The Group element notation in this specification is as definedin the Periodic Table of Elements according to the IUPAC 1988 notation(IUPAC Nomenclature of Inorganic Chemistry 1960, Blackwell Publ.,London). Therein, Groups 4, 5, 8, 9 and 15 correspond respectively toGroups IVB, VB, IIIA, IVA and VA of the Deming notation (Chemical RubberCompany's Handbook of Chemistry & Physics, 48th edition) and to GroupsIVA, VA, IIIB, IVB and VB of the IUPAC 1970 notation (Kirk-OthmerEncyclopedia of Chemical Technology, 2nd edition, Vol. 8, p. 94).Non-limiting examples of supports include inorganic oxides such assilica, alumina, titania, zirconia, thoria, as well as mixtures of suchoxides such as, for example, silica-chromium, silica-alumina,silica-titania, and the like.

Inorganic oxide materials, which may be used as a support in thecatalyst compositions of the present disclosure, are porous materialshaving variable surface area and particle size. The support may have asurface area in a range of 50 to 1000 square meters per gram, and anaverage particle size of 20 to 300 micrometers. In one or moreembodiments, the support may have a pore volume of about 0.5 to about6.0 cm³/g and a surface area of about 200 to about 600 m²/g. In one ormore embodiments, the support may have a pore volume of about 1.1 toabout 1.8 cm³/g and a surface area of about 245 to about 375 m²/g. Inone or more embodiments, the support may have a pore volume of about 2.4to about 3.7 cm³/g and a surface area of about 410 to about 620 m²/g. Inone or more embodiments, the support may have a pore volume of about 0.9to about 1.4 cm³/g and a surface area of about 390 to about 590 m²/g.Each of the above properties may be measured using conventionaltechniques as known in the art.

The support may comprise silica, including amorphous silica, and highsurface area amorphous silica. Such support materials are commerciallyavailable from a number of sources. Such sources include the W.R. Graceand Company which markets silica support materials under the trade namesof Sylopol 952 or Sylopol 955, and PQ Corporation, which markets silicasupport materials under various trade designations, including ES70. Thesilica can be in the form of spherical particles, which are obtained bya spray-drying process, for example. Alternatively, PQ Corporationmarkets silica support materials under trade names such as MS3050 whichare not spray-dried. As procured, these silicas are not calcined, i.e.,not dehydrated. However, silica that is calcined prior to purchase maybe used in catalysts of the present disclosure.

Supported chromium compounds, such as chromium acetate, which arecommercially available, may also be used as a catalyst. Commercialsources include the W.R. Grace and Company, which provides chromium onsilica support materials under trade names such as Sylopol 957, Sylopol957HS, or Sylopol 957BG, and PQ Corporation, which provides chromium onsilica support materials under various trade names, such as ES370. Thechromium on silica support can be in the form of spherical particles,which are obtained by a spray-drying process. Alternatively, PQCorporation provides chromium on silica support materials under tradenames such as C35100MS and C35300MS, which are not spray-dried. Asprocured, these silicas are not activated. However, if available,chromium supported on silica that is activated prior to purchase may beused in catalysts of the present disclosure.

Activation of a supported chromium oxide catalyst can be accomplished atvarious temperatures, e.g., from about 300° C. up to a temperature atwhich substantial sintering of the support takes place. For example,activated catalysts may be prepared in a fluidized-bed, as follows. Thepassage of a stream of dry air or oxygen through a supportedchromium-based catalyst during the activation aids in the displacementof any water from the support and converts, at least partially, chromiumspecies to Cr+6.

Temperatures used to activate the chromium oxide-based catalysts can behigh enough for rearrangement of the chromium compound on the supportmaterial. Peak activation temperatures of from about 300° C. to about900° C. for periods of from greater than 1 hour to as high as 48 hourscan be utilized. The supported chromium oxide catalysts may be activatedat temperatures from about 400° C. to about 850° C., from about 500° C.to about 700° C., or from about 550° C. to about 650° C. For one or moreembodiments, the activation temperatures are about 600° C., about 700°C., or about 800° C. The supported chromium oxide catalysts may beactivated at a chosen peak activation temperature for a period of fromabout 1 to about 36 hours, from about 3 to about 24 hours, or from about4 to about 6 hours. For one or more embodiments, peak activation timesare about 4 hours, or about 6 hours. Activation can be performed in anoxidative environment; for example, well dried air or oxygen can be usedand the temperature can be maintained below the temperature at whichsubstantial sintering of the support occurs. After the chromiumcompounds are activated, a powdery, free-flowing particulate chromiumoxide catalyst is produced.

The cooled, activated chromium oxide catalyst may then be slurried andcontacted with a reducing agent, fed at a selected feed rate over aselected time period, to result in a catalyst composition having apolymer flow index response within a selected range. The solvent maythen be substantially removed from the slurry to result in a dried,free-flowing catalyst powder, which may be fed to a polymerizationsystem as is or slurried in a suitable liquid prior to feeding.

In one or more embodiments, because organometallic components utilizedin preparation of the catalysts described herein may react with water,the support material should preferably be substantially dry. Forexample, where the chromium-based catalysts are silyl chromates, theuntreated supports may be dehydrated or calcined prior to contactingwith the chromium-based catalysts.

The support may be calcined at elevated temperatures to remove water,and/or to effectuate a chemical change on the surface of the support.Calcination of the support can be performed using a procedure known tothose of ordinary skill in the art.

For example, calcined silica may be prepared in a fluidized-bed, asfollows. A silica support material, e.g. Sylopol 955, may be heated insteps or steadily from ambient temperature to the desired calciningtemperature. e.g., 600° C., while passing dry nitrogen or dry airthrough or over the support material. The silica can be maintained atabout this temperature for about 1 to about 4 hours, after which it isallowed to cool to ambient temperature. The calcination temperature mayaffect the number of OH groups on the support surface; i.e., the numberof OH groups on the support surface (silanol groups in the case ofsilica) is approximately inversely proportional to the temperature ofdrying or dehydration: the higher the temperature, the lower thehydroxyl group content.

Supports may be calcined at a peak temperature from about 350° C. toabout 850° C., from about 400° C. to about 700° C., or from about 500°C. to about 650° C. Calcination times may be from about 2 hours to about24 hours, from about 4 hours to about 16 hours, from about 8 hours toabout 12 hours.

The silyl chromate compound may be contacted with the calcined supportto form a “bound catalyst.” The silyl chromate compound may be contactedwith the calcined support material in a procedure known to one ofordinary skill in the art. The silyl chromate compound may be contactedwith the support as in a solution, slurry, or solid form, or somecombination thereof, and may be heated to any desirable temperature, fora specified time sufficient to effectuate a desirable chemical/physicaltransformation.

This contacting and transformation can be conducted in a non-polarsolvent. Suitable non-polar solvents may be materials which are liquidat contacting and transformation temperatures and in which some of thecomponents used during the catalyst preparation, i.e., silyl chromatecompounds and reducing agents are at least partially soluble. Thenon-polar solvents may be alkanes, particularly those containing about 5to about 10 carbon atoms, such as pentane, isopentane, hexane,isohexane, n-heptane, isoheptane, octane, nonane, and decane. They maybe cycloalkanes, particularly those containing about 5 to about 10carbon atoms, such as cyclohexane and methylcyclohexane, may also beused. The non-polar solvent may also be a solvent mixture. The non-polarsolvent may be purified prior to use, such as by degassing under vacuumand/or heat or by percolation through silica gel and/or molecularsieves, to remove traces of water, molecular oxygen, polar compounds,and other materials capable of adversely affecting catalyst activity. Areducing agent may then be contacted with the slurry, where the reducingagent is fed at a selected feed rate over a selected time period toresult in a catalyst having a flow index response within a selectedrange. Alternatively, after supporting the silyl chromate compound onthe support, and before adding the reducing agent, the solvent may thenbe substantially removed by evaporation, to yield a free-flowingsupported silyl chromate on support. The thus supported silyl chromatemay be re-slurried in the same or a different non-polar solvent andcontacted with a reducing agent to result in a selected flow indexresponse.

Once the catalyst is supported, and in the case of chromium oxidecatalysts, activated, the chromium-based catalyst composition may thenbe slurried in a non-polar solvent, prior to the addition of thereducing agent. The supported catalyst may be chromium oxide supportedcatalysts, silyl chromate catalysts, or a mixture of both. This slurryis prepared by admixture of the supported catalyst with the non-polarsolvent. In some embodiments, the supported silyl chromate compound isnot dried before the addition of the reducing agent.

The chromium-based catalysts of the present disclosure can be contactedwith a reducing agent. Reducing agents include organoaluminum compoundssuch as aluminum alkyls and alkyl aluminum alkoxides, for instance.Alkyl aluminum alkoxides, of the general formula R₂AlOR, may be suitablefor use in embodiments of this disclosure. The R or alkyl groups of theabove general formula may be the same or different, may have from about1 to about 12 carbon atoms in some embodiments, about 1 to about 10carbon atoms in other embodiments, about 2 to about 8 carbon atoms inyet other embodiments, and about 2 to about 4 carbon atoms in furtherembodiments. Examples of the alkyl aluminum alkoxides include, but arenot limited to, diethylaluminum methoxide, diethylaluminum ethoxide(DEAlE), diethylaluminum propoxide, diethylaluminum iso-propoxide,diethylaluminum tert-butoxide, dimethylaluminum ethoxide, di-isopropylaluminum ethoxide, di-isobutyl aluminum ethoxide, methyl ethyl aluminumethoxide and mixtures thereof.

The reducing agent may be added to a mixture of a supported chromatecatalyst with a non-polar solvent. The reducing agent may be added to amixture of an activated chromium oxide catalyst with a non-polarsolvent. The reducing agent may be added to a mixture of silyl chromatecatalysts and activated chromium oxide-based catalyst in a non-polarsolvent. When both chromium oxide-based catalysts and silylchromate-based catalysts are utilized, each catalyst may be deposited ona separate support and have respective calcination and/or activationtreatments prior to mixing together. Addition of the reducing agent tothe catalyst slurry may be conducted at elevated temperatures and underan inert atmosphere, such as up to 7 bar (100 psig) nitrogen headpressure. For example, the slurry may be maintained at a temperaturebetween about 30° C. and 80° C. during admixture of the reducing agent,at a temperature between about 40° C. and about 60° C., or at atemperature between about 40° C. and about 50° C.

Chromium-based catalysts formed by the described processes may have achromium loading, e.g., on the support, ranging from about 0.15 to about3 weight percent based on the total weight of the catalyst; from about0.2 to about 0.3 weight percent; from about 0.4 to about 0.6 weightpercent; or from 0.7 to about 1.2 weight percent. Chromium-basedcatalysts formed by the described processes may have a reducing agent tochromium molar ratio ranging from about 0.5 to about 8 in someembodiments; from about 2 to about 7 in other embodiments; and fromabout 3.0 to about 5.5 in yet other embodiments.

A number of embodiments of the present disclosure provide thatchromium-based catalysts formed by the described processes may have analuminum loading, e.g., on the support, ranging from about 0.15 to about3 weight percent based on the total weight of the catalyst; from about0.2 to about 0.3 weight percent; from about 0.4 to about 0.6 weightpercent; or from 0.7 to about 2.0 weight percent. Chromium-basedcatalysts formed by the described processes may have a reducing agent toaluminum molar ratio ranging from about 0.5 to about 8 in someembodiments; from about 1 to about 7 in other embodiments; and fromabout 2.0 to about 5.5 in yet other embodiments.

A number of embodiments of the present disclosure provide that one ormore additives may be utilized in forming the polymers. The polymers mayinclude about 0.1 wt % to about 40 wt %, or 5 wt % to about 25 wt %, forexample, of the one or more additives, based on a total weight of theresulting polymer. Examples of such additives include, but are notlimited to, tackifiers, waxes, functionalized polymers such as acidmodified polyolefins and/or anhydride modified polyolefins, antioxidants(e.g., hindered phenolics such as IRGANOX™ 1010 or IRGANOX™ 1076available from Ciba-Geigy), (e.g., IRGAFOS™ 168 available fromCiba-Geigy), oils, compatabilizers, fillers, adjuvants, adhesionpromoters, plasticizers, low molecular weight polymers, blocking agents,antiblocking agents, anti-static agents, release agents, anti-clingadditives, colorants, dyes, pigments, processing aids, UV stabilizers,heat stabilizers, neutralizers, lubricants, surfactants, nucleatingagents, flexibilizers, rubbers, optical brighteners, colorants,diluents, viscosity modifiers, oxidized polyolefins, and any combinationthereof, among others.

The polymers may be formed by suspension, solution, slurry, and/or gasphase processes, using known equipment and reaction conditions. Polymerformation is not limited to any specific type of polymerization system.As an example, olefin polymerization temperatures may range from about0° C. to about 300° C. at atmospheric, sub-atmospheric, orsuper-atmospheric pressures. In particular, slurry or solutionpolymerization systems may employ sub-atmospheric, or alternatively,super-atmospheric pressures, and temperatures in the range of about 40°C. to about 300° C.

A number of embodiments of the present disclosure provide that thepolymers may be formed via a gas phase polymerization system, atsuper-atmospheric pressures in the range from 0.07 to 68.9 bar (1 to1000 psig), from 3.45 to 27.6 bar (50 to 400 psig), or from 6.89 to 24.1bar (100 to 350 psig), and a temperature in the range from 30° C. to130° C., from 65° C. to 110° C., from 75° C. to 120° C., or from 80° C.to 120° C. For a number of embodiments, operating temperatures may beless than 112° C. Stirred and/or fluidized bed gas phase polymerizationsystems may be utilized.

Generally, a conventional gas phase, fluidized bed process can beconducted by passing a stream containing one or more olefin monomerscontinuously through a fluidized bed reactor under reaction conditionsand in the presence of a catalyst composition at a velocity sufficientto maintain a bed of solid particles in a suspended state. A streamcomprising unreacted monomer can be continuously withdrawn from thereactor, compressed, cooled, optionally partially or fully condensed,and recycled back to the reactor. Product, i.e., polymer, can bewithdrawn from the reactor and replacement monomer can be added to therecycle stream. Gases inert to the catalyst composition and reactantsmay also be present in the gas stream. The polymerization system mayinclude a single reactor or two or more reactors in series, for example.

Feed streams may include olefin monomer, non-olefinic gas such asnitrogen and/or hydrogen, and may further include one or morenon-reactive alkanes that may be condensable in the polymerizationprocess and used for removing the heat of reaction. Illustrativenon-reactive alkanes include, but are not limited to, propane, butane,isobutane, pentane, isopentane, hexane, isomers thereof and derivativesthereof. Feeds may enter the reactor at a single or multiple anddifferent locations.

A number of embodiments of the present disclosure provide that oxygenmay be added to the polymerization at a concentration relative to theethylene feed rate to the reactor of about 10 to 600 parts per billionvolume (ppbv), and more preferably about 10 to 500 ppbv. For instance,oxygen can be added at a concentration of 20 ppbv continuously to areactor recirculation line at a point upstream of a cycle gascompressor, which is also upstream of a cycle gas heat exchanger, e.g.,a cooler. This oxygen may help to reduce fouling of the cycle line,compressor and/or the heat exchanger with polymer.

Organometallic compounds may be employed as scavenging agents to removecatalyst poisons, thereby increasing the catalyst activity, or for otherpurposes. Examples of organometallic compounds that may be added includemetal alkyls, such as aluminum alkyls. Conventional additives may alsobe used in the process.

An illustrative catalyst reservoir suitable for continuously feeding drycatalyst powder into the reactor is shown and described in U.S. Pat. No.3,779,712, for example. A gas that is inert to the catalyst, such asnitrogen or argon, can be used to carry the catalyst into the reactorbed. In another embodiment, the catalyst can be provided as a slurry inmineral oil or liquid hydrocarbon or mixture such, as for example,propane, butane, isopentane, hexane, heptane or octane. An illustrativecatalyst reservoir is shown and described in WO 2004/094489. Thecatalyst slurry may be delivered to the reactor with a carrier fluid,such as, for example, nitrogen or argon or a liquid such as for exampleisopentane or other C₃ to C₈ alkanes.

FIG. 1 illustrates an example of a portion of a polymerization system150 in accordance with one or more embodiments of the presentdisclosure. The polymerization system 150 can include a reactor 160 influid communication with one or more discharge tanks 175 (only oneshown), surge tanks 180 (only one shown), and recycle compressors 190(only one shown). The polymerization system 150 can also include morethan one reactor 160, e.g., arranged in series, parallel, or configuredindependently from the other reactors. Each reactor may have its ownassociated tanks 175, 180 and compressors 190 or alternatively, mayshare any one or more of the associated tanks 175, 180 and compressors190. For simplicity and ease of description, embodiments of the presentdisclosure will be further described in the context of a single reactortrain.

In one or more embodiments, the reactor 160 can include a reaction zone162 in fluid communication with a velocity reduction zone 164. Thereaction zone 162 can include a bed of growing polymer particles, formedpolymer particles, and catalyst particles fluidized by the continuousflow of polymerizable and modifying gaseous components in the form ofmake-up feed and recycle fluid through the reaction zone 162.

A feedstream 105 can be directed to enter the cycle line before thecompressor 190, but may also be located at any point in thepolymerization system 150, including to the reactor fluid bed, theexpanded section or to the cycle line before or after the cooler, e.g.,as illustrated with alternative feedstream location 147. The term “feedstream” as used herein refers to a raw material, either gas phase orliquid phase, used in a polymerization process to produce a polymerproduct. For example, a feed stream may comprise a monomer as discussedherein. For instance, a feedstream may comprise an olefin monomerincluding substituted and unsubstituted alkenes having two to 12 carbonatoms, such as ethylene, propylene, 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, styrene,derivatives thereof, and combinations thereof. The feed stream may alsoinclude a non-olefinic gas such as nitrogen and hydrogen. Feed streamsmay enter the reactor at multiple and different locations. For example,monomers can be introduced into the polymerization zone in various waysincluding direct injection through a nozzle (not illustrated) into thebed. A feed stream may further include one or more non-reactive alkanes,e.g., that may be condensable in the polymerization process, forremoving the heat of reaction. Non-reactive alkanes include, but are notlimited to, propane, butane, isobutane, pentane, isopentane, hexane,isomers thereof, derivatives thereof, and combinations thereof.

For polymerization utilizing a chromium-based catalyst, including thosemodified with aluminum alkyls, hydrogen may be added at a gas mole ratioof hydrogen to ethylene in the reactor that can be in a range of about0.0 to 0.5, in a range of 0.01 to 0.4, in a range of 0.03 to 0.3, or ina range of 0.005 to 0.020. A number of embodiments of the presentdisclosure utilize hydrogen gas. The hydrogen can affect the molecularweight and/or distribution of the polymer and may influence polymerproperties.

During polymerization, the fluidized bed can have a general appearanceof a dense mass of individually moving particles as created by thepercolation of gas through the bed. A pressure drop through the bed canbe equal to or slightly greater than a weight of the bed divided by across-sectional area. In other words, it can be dependent on thegeometry of the reactor 160. To maintain a viable fluidized bed in thereaction zone 162, a superficial gas velocity through the bed can exceeda minimum flow velocity for fluidization. The superficial gas velocitycan be at least two times the minimum flow velocity. For a number ofembodiments, the superficial gas velocity does not exceed 5.0 ft/sec(1.52 m/sec). For a number of embodiments, the superficial gas velocitywill be no more than 2.5 ft/sec (0.76 m/sec).

According to a number of embodiments, a height to diameter ratio of thereaction zone 162 can be in the range of from about 2:1 to about 5:1.The range may vary to larger or smaller ratios, e.g., depending upon adesired production capacity. A cross-sectional area of the velocityreduction zone 164 can be within the range of about 2 to about 3multiplied by the cross-sectional area of the reaction zone 162, forexample.

The velocity reduction zone 164 has a larger inner diameter than thereaction zone 162. As the name suggests, the velocity reduction zone 164slows the velocity of the gas due to the increased cross sectional area.This reduction in gas velocity drops the entrained particles into thebed, allowing primarily only gas to flow from the reactor 160. That gasexiting the overhead of the reactor 160 is a recycle gas stream 149.

The recycle stream 149 can be compressed in a compressor 190 and thenpassed through a heat exchange zone where heat is removed before it isreturned to the bed. The heat exchange zone can be a heat exchanger 192,which can be of the horizontal or vertical type, for example. Severalheat exchangers can be employed to lower the temperature of the cyclegas stream in stages. It is also possible to locate the compressordownstream from the heat exchanger or at an intermediate point betweenseveral heat exchangers. After cooling, the recycle stream can bereturned to the reactor 160. The cooled recycle stream can absorb theheat of reaction generated by the polymerization reaction.

The recycle stream can be returned to the reactor 160 and to thefluidized bed through a gas distributor plate 195. A gas deflector 196can be installed at the inlet to the reactor 160, e.g., to reducecontained polymer particles from settling out and agglomerating into asolid mass and/or to reduce liquid accumulation at the bottom of thereactor, as well to facilitate easy transitions between processes whichcontain liquid in the cycle gas stream and those which do not and viceversa. An illustrative deflector suitable for this purpose is describedin U.S. Pat. Nos. 4,933,149 and 6,627,713, for instance.

An activated precursor composition, with or without an aluminum alkylmodifier, which collectively can be referred to as catalyst, can bestored for service in a catalyst reservoir 155 under a blanket of a gaswhich is inert to the stored material, such as nitrogen or argon. Thecatalyst reservoir 155 can be equipped with a feeder suitable tocontinuously feed the catalyst into the reactor 160. An illustrativecatalyst reservoir is shown and described in U.S. Pat. No. 3,779,712,for example. A gas that is inert to the catalyst, such as nitrogen orargon, can be used to carry the catalyst into the bed. The carrier gascan be the same as the blanket gas used for storing the catalysts in thecatalyst reservoir 155. In one embodiment, the catalyst is a dry powderand the catalyst feeder comprises a rotating metering disk. In anotherembodiment, the catalyst is provided as a slurry in mineral oil orliquid hydrocarbon or mixture such as for example propane, butane,isopentane, hexane, heptane or octane. An illustrative catalystreservoir is shown and described in WO 2004094489. The catalyst slurrymay be delivered to the reactor with a carrier fluid, such as, forexample, nitrogen or argon or a liquid such as for example isopentane orother C₃ to C₈ alkane.

The catalyst can be injected at a point into the bed where good mixingwith polymer particles occurs, for example. For instance, the catalystcan be injected into the bed at a point above the distributor plate 195.Injecting the catalyst at a point above the distribution plate 195 canprovide satisfactory operation of a fluidized-bed polymerizationreactor, e.g., reactor 160. Injection of the catalyst into the areabelow the distributor plate 195 may cause polymerization to begin thereand eventually cause plugging of the distributor plate 195. Injectiondirectly into the fluidized bed can aid in distributing the catalystuniformly throughout the bed and may help reduce the formation oflocalized spots of high catalyst concentration which can cause “hotspots” to form. Injection of the catalyst into the reactor 160 above thebed can result in excessive catalyst carryover into the recycle line149, where polymerization could occur leading to plugging of the line149 and/or heat exchanger 192.

A density modifier compound, e.g., an aluminum alkyl compound,non-limiting illustrative examples of which are triethyl aluminum anddiethyl aluminum ethoxide, can be added to the reaction system 150either directly into the fluidized bed or downstream of the heatexchanger 192, in which case the density modifier compound is fed intothe recycle system from a dispenser 156. The amount of density modifiercompound added to the polymerization reactor when using the chromiumbased catalyst can be in a range of about 0.005 to about 10 densitymodifier compound to chromium on a molar basis, in a range of about 0.01to 5, in a range of about 0.03 to 3, or in a range of 0.05 to 2.Utilizing the density modifier compound may provide a fluidized bulkdensity and/or settled bulk density of the polymer that may be depressedby about 2 to 4 lb/ft³.

The polymerization reaction can be conducted substantially in theabsence of catalyst poisons such as moisture, oxygen, and acetylene.However, oxygen can be added back to the reactor 160 at very lowconcentrations to alter the polymer structure and its productperformance characteristics. Oxygen may be added at a concentrationrelative to the ethylene feed rate to the reactor of about 10 to 600ppbv, and more preferably about 10 to 500 ppbv.

A number of embodiments provide that co-monomers are polymerized withethylene from about 0 to anywhere from 5, 10 or 20 weight percent of theco-monomer in the copolymer to achieve a desired density range of thecopolymers. The amount of co-monomer can depend on the particularco-monomer(s) being utilized, the catalyst composition, the molar ratioof aluminum to chromium, catalyst preparation conditions, and/orreaction temperature. The ratio of the co-monomer to ethylene feed ratioand/or gas mole ratio can be controlled to obtain the desired resindensity of copolymer product.

A gas analyzer 151 can be used to determine the composition of therecycle stream and the composition of the stream 105 and 147, and can beadjusted accordingly to maintain an essentially steady state gaseouscomposition within the reaction zone 162. The gas analyzer 151 can be aconventional gas analyzer that determines the recycle stream compositionto maintain the ratios of feed stream components. Such equipment iscommercially available from a wide variety of sources. The gas analyzer151 may be positioned to receive gas from a sampling point locatedbetween the velocity reduction zone 164 and heat exchanger 192.

A rate of polymer production in the bed can depend on a rate of catalystinjection and a concentration of monomer(s) in the reaction zone. Theproduction rate can be controlled by adjusting the rate of catalystinjection, for instance. Since a change in the rate of catalystinjection can change the reaction rate and thus the rate at which heatis generated in the bed, the temperature of the recycle stream enteringthe reactor can be adjusted to accommodate any change in the rate ofheat generation. This help to provide an essentially constanttemperature in the bed. Complete instrumentation of both the fluidizedbed and the recycle stream cooling system is, of course, useful todetect any temperature change in the bed so as to enable either anoperator or a conventional automatic control system to adjust thetemperature of the recycle stream.

Under a given set of operating conditions, the fluidized bed ismaintained at essentially a constant height by withdrawing a portion ofthe bed as product at the rate of formation of the polymer product.Since the rate of heat generation is directly related to the rate ofproduct formation, a measurement of the temperature rise of the fluidacross the reactor, e.g., a difference between inlet fluid temperatureand exit fluid temperature, is indicative of the rate of polymerformation at a constant fluid velocity if no or negligible vaporizableliquid is present in the inlet fluid, for instance.

According to a number of embodiments, on discharge of polymer productfrom the reactor 160, it can be preferable to separate fluid from theproduct and to return the fluid to the recycle line 149. There are anumber of ways known to the art to accomplish this separation. In one ormore embodiments, fluid and product leave the reactor 160 and enter theproduct discharge tanks 175 (one is illustrated) through valve 177,which may be a ball valve designed to have minimum restriction to flowwhen opened. Positioned above and below the product discharge tank 175are conventional valves 178, 179. The valve 179 allows passage ofproduct into the product surge tanks 180 (one is illustrated).

In one or more modes of operation, valve 177 is open and valves 178,179are in a closed position. Product and fluid enter the product dischargetank 175. Valve 177 closes and the product is allowed to settle in theproduct discharge tank 175. Valve 178 is then opened permitting fluid toflow from the product discharge tank 175 to the reactor 162. Valve 178is then closed and valve 179 is opened and any product in the productdischarge tank 175 flows into the product surge tank 180. Valve 179 isthen closed. Product is then discharged from the product surge tank 180through valve 184. The product can be further purged to remove residualhydrocarbons and conveyed to storage or compounding. The particulartiming sequence of the valves 177, 178, 179, 184 is accomplished by theuse of conventional programmable controllers which are well known in theart.

Another example of a product discharge system, which may bealternatively employed, is disclosed in U.S. Pat. No. 4,621,952. Such asystem employs at least one (parallel) pair of tanks comprising asettling tank and a transfer tank arranged in series and having theseparated gas phase returned from the top of the settling tank to apoint in the reactor near the top of the fluidized bed.

The fluidized-bed reactor 160 can be equipped with a venting system (notillustrated) to provide venting of the bed during start up and shutdown. The reactor 160 does not require the use of stirring and/or wallscraping. The recycle line 149 and the elements therein, e.g.,compressor 190 and heat exchanger 192, etc., can be smooth surfaced anddevoid of unnecessary obstructions so as not to impede the flow ofrecycle fluid or entrained particles.

Various techniques for preventing fouling of the reactor and polymeragglomeration can be used. Illustrative of these techniques are theintroduction of finely divided particulate matter to preventagglomeration, as described in U.S. Pat. Nos. 4,994,534 and 5,200,477;the addition of negative charge generating chemicals to balance positivevoltages or the addition of positive charge generating chemicals toneutralize negative voltage potentials as described in U.S. Pat. No.4,803,251, for instance. Antistatic substances may also be added, eithercontinuously or intermittently to prevent or neutralize electrostaticcharge generation. Condensing mode operation such as disclosed in U.S.Pat. Nos. 4,543,399 and 4,588,790 can also be used to assist in heatremoval from the fluid bed polymerization reactor.

The conditions for polymerizations vary depending upon the monomers,catalysts and equipment availability. The specific conditions are knownor readily derivable by those skilled in the art. For example, thetemperatures may be in the range from 30° C. to 130° C., from 65° C. to110° C., from 75° C. to 120° C., or from 80° C. to 120° C. For one ormore embodiments, operating temperatures may be less than 112° C. Anumber of embodiments of this disclosure provide gas phasepolymerization systems, at super-atmospheric pressures in the range from0.07 to 68.9 bar (1 to 1000 psig), from 3.45 to 27.6 bar (50 to 400psig), or from 6.89 to 24.1 bar (100 to 350 psig). Additional knowndetails of polymerization are described in U.S. Pat. No. 6,627,713,which is incorporated by reference.

EXAMPLES

In the Examples, various terms and designations for materials are usedincluding, for instance, the following:

Carbon dioxide (flow index modifier, 10,000 ppm in nitrogen, availablefrom Airgas, Inc.); carbon monoxide (flow index modifier, 5,000 ppm innitrogen, available from Airgas, Inc.); 2,4-hexadiene (flow indexmodifier, diluted in hexane, 90% technical grade, CAS 592-46-1,available from Sigma-Aldrich); alkyl aluminum alkoxide (DEAlE inisopentane, available from Akzo Nobel).

Silyl chromate catalysts (startup catalyst) were prepared as follows.Porous silica support (Grade Sylopol 955 silica produced by DavisonCatalyst division of W. R. Grace and Co; particle size approximately 40microns; surface area of approximately 300 square meters per gram) wascharged to a fluidized bed heating vessel and heated at a rate ofapproximately 100° C. per hour under dry nitrogen to approximately 325°C. The nitrogen stream was then replaced with a stream of dry air andthe support was heated at a rate of about 100° C. per hour toapproximately 600° C., where it was maintained for approximately 1.5 to4 hours. Thereafter, the support was cooled with dry, ambienttemperature air to approximately 300° C. and then further cooled to roomtemperature with dry, ambient temperature nitrogen to provide a powder,which was stored under nitrogen atmosphere until further processing.

The support, as described above, was placed in a vertical catalystblender with a double helical ribbon agitator under an inert atmosphere.Approximately 5.8 liters of degassed and dried hexane solvent werecharged per kilogram (0.70 gallons per pound) of silica. The resultingmixture was stirred and heated to approximately 45° C. Thereafter, 3.15kilograms of bis(triphenylsilyl) chromate powder was charged for every100 kilograms of silica; then stirred for 10 hours while maintained atabout 45° C. to provide a slurry. Thereafter, a 25 wt % solution ofDEAlE in isopentane was added above the surface of the slurry in lessthan 10 minutes to provide a selected molar ratio of DEAlE/Cr. Themixture was agitated at 30 rpm at a temperature of approximately 45° C.during the addition time and thereafter for approximately 2 hours.Thereafter, the solvent was substantially removed by drying at a jackettemperature of approximately 60° C. for about 18 to 24 hours at slightlyabove atmospheric pressure to provide the silyl chromate catalysts. Thesilyl chromate catalyst (a dry, free flowing powder) was then storedunder nitrogen until used.

Reduced chromium oxide catalysts were prepared as follows. Porous silicasupport containing approximately 5 wt % chromium acetate (GradeC35300MSF chromium on silica; particle size of approximately 82 microns;surface area of approximately 500 square meters per gram; produced by PQCorporation) to provide approximately 1 wt % Cr, was charged to afluidized bed heating vessel. Therein, the chromium on silica was heatedat a rate of approximately 50° C. per hour under dry nitrogen up to 200°C. and maintained at that temperature for approximately 4 hours.Thereafter, the chromium on silica was heated at a rate of approximately50° C. per hour under dry nitrogen up to 450° C. and maintained at thattemperature for approximately 2 hours. The nitrogen stream was thenreplaced with a stream of dry air and the chromium on silica was heatedat a rate of approximately 50° C. per hour to 600° C., where it wasmaintained for about 6 hours for activation. The activated chromium onsilica was then cooled with ambient temperature dry air to approximately300° C. and then further cooled to room temperature with dry, ambienttemperature nitrogen. The activated chromium on silica was placed in avertical catalyst blender with a double helical ribbon agitator under aninert atmosphere. Dried isopentane solvent was added to the verticalcatalyst blender to provide a slurry. Thereafter, a 25 wt % solution ofDEAlE in isopentane was added above the surface of the slurry over anapproximate 40 to 60-minute time period to provide a selected aluminumloading weight percent. The slurry was agitated at 30 rpm at atemperature of approximately 45° C. during the addition time andthereafter for approximately 2 hours. Thereafter, solvent wassubstantially removed by drying at a jacket temperature approximately60° C. to 70° C. for about 18 to 21 hours at slightly above atmosphericpressure to provide the reduced chromium oxide catalysts. The reducedchromium oxide catalyst (a dry, free flowing powder) was then storedunder nitrogen until used.

Comparative Example A was performed as follows. A 60 kg silyl chromatecatalystpolymerized seed bed was loaded to a UNIPOL™ pilot plant gasphase fluid bed reactor. The reactor comprised a vertical cylinder witha nominal pipe size of about 14 inches, followed by a freeboard,diameter transition spool piece and an expanded section. In operation,fluidizing gas was circulated in a continuous loop entering thefluidized bed from below through a distributor plate, passing throughthe bed and out the top of the reactor to a cycle gas compressor(blower) and then through a shell and tube cooler to control the bedpolymerization temperature. Superficial gas velocity was calculatedcontinuously through the bed and maintained with a ball valve andventuri assembly in the cycle line. Concentration of monomers andreactive/non-reactive gases was monitored by a chromatograph thatsampled the gas every 1 to 5 minutes. Ethylene partial pressure wasmeasured and controlled by a DCS (Distributed Control System), as werethe hydrogen and any comonomer levels that were converted to gas moleratio to ethylene partial pressure for controlling the polymer flowindex and the polymer density. Total reactor pressure was essentiallyconstant and controlled with make-up nitrogen or by additional venting.Polymer was discharged periodically from the reactor through a firstvalve to a receiving tank where it was purged with nitrogen to reducethe concentration of monomers before being released through a secondvalve to a fiber-pak drum exposed to the atmosphere.

The reactor and seed bed were dried to less than 2 ppm water at hightemperature, followed by a passivation period with a dilute solution oftrimethylaluminum (TMA) at high temperature to remove trace water andother impurities. Thereafter, a series of nitrogen purge cycles wereperformed, followed by the addition of a low level of carbon dioxide athigh temperature to react with residual TMA. Gas compositions andtemperature for polymerization were then established in the reactor andthe catalyst feed initiated. Dilute triethylaluminum in isopentane wasthen fed to the reactor for approximately 48 hours to sustain the silylchromate catalyst reaction as impurities were removed. Thereafter, thereactor was maintained at a temperature of 110° C. for 6 days. Thisreactor startup was longer than expected, e.g., a polymerizationreaction can generally be started after the inside of the reactor hasbeen exposed to air (during a reactor shut-down), that does not utilizeTEAl and/or a protracted period of time of higher temperature operationto remove impurities, as described for Comparative Example A. Then, thereactor was transitioned to the reduced chromium oxide catalysts and thefollowing reactor conditions were maintained: reactor temperature of108° C., H₂/C₂ gas mole ratio of 0.15, C₆/C₂ gas mole ratio of 0.036,and an average residence time of the bed in the reactor of 2.3 hours.The bed weight was adjusted to maintain the bed level in the reactorbetween 8-9 feet and an anti-fouling stream of dilute oxygen in nitrogen(oxygen add-back) was maintained at 0.020 ppm on an ethylene feed basisto the cycle line before the cycle gas compressor, which was upstream ofthe cycle gas shell and tube heat exchanger (water on the shell side)for the bed temperature control. For some polymerizations, oxygen mayprovide a flow index increase with increasing oxygen concentrations;however, oxygen was utilized for each Example and Comparative Exampleherein. FIGS. 4 through 7 respectively illustrate polymer flow index,catalyst productivity, polymer density, and fluidized bulk density forComparative Example A (0.020 ppm oxygen polymerization, i.e. at 0.0 ppmof the polymer flow index modifier described herein).

Comparative Example B was performed as Comparative Example A with thechange that carbon dioxide was utilized at a reactor concentration of0.20 ppm carbon dioxide based upon ethylene feed, a concentration lessthan the active amount described herein, and introduced via apressurized cylinder of the carbon dioxide diluted in nitrogen that wasmetered to the reactor through a low flow rate Brooks Instrument 5850EMass Flow Controller. Flow index additive concentration was adjustedrelative to the reactor ethylene feed rate on a molar basis.

Example 1, a process for modifying a polymer flow index, was performedas Comparative Example B with the change that the carbon dioxide wasutilized at a reactor concentration of 25.0 ppm carbon dioxide basedupon the ethylene feed.

Example 2, a process for modifying a polymer flow index, was performedas Comparative Example B with the change that carbon monoxide at areactor concentration of 0.20 ppm carbon monoxide based upon theethylene feed was utilized rather than the carbon dioxide diluted innitrogen.

Example 3, a process for modifying a polymer flow index, was performedas Comparative Example B with the change that the carbon monoxide wasutilized at a reactor concentration of 0.51 ppm carbon monoxide basedupon the ethylene feed rather than the carbon dioxide diluted innitrogen.

Example 4, a process for modifying a polymer flow index, was performedas Comparative Example B with the change that 2,4-hexadiene diluted inhexane was utilized rather than the carbon dioxide diluted in nitrogen.The 2,4-hexadiene diluted in hexane was utilized at a reactorconcentration of 0.69 ppm 2,4-hexadiene based upon the ethylene feed andwas added directly to the reactor via a ⅛ inch injection tube, meteredfrom two Teledyne ISCO Model 100DM Syringe Pumps (single pump, 103 mlcapacity, 25 ml/min maximum flow, 0.00001 ml/min minimum flow) withTeledyne ISCO Series D Pump Controllers.

Example 5, a process for modifying a polymer flow index, was performedas Example 4 with the change that the 2,4-hexadiene diluted in hexanewas utilized at a reactor concentration of 2.78 ppm 2,4-hexadiene basedupon the ethylene feed.

For Comparative Examples A-B: concentration of carbon dioxide; reactortemperature; H₂/C₂ mole ratio; C₆/C₂ mole ratio; and residence time areshown in Table 1. For Examples 1-5: concentration of carbon dioxide,carbon monoxide, and 2,4-hexadiene; reactor temperature; H₂/C₂ moleratio; C₆/C₂ mole ratio; and residence time are shown in Table 2

TABLE 1 Concentration Reactor H₂/C₂ C₆/C₂ (ppmv based Temperature molemole Residence on ethylene (° C.) ratio ratio time (hrs) feed)Comparative 108 0.15 0.036 2.3 0.00 Example A Comparative 108 0.15 0.0362.3 0.20 Example B (Carbon Dioxide)

TABLE 2 Concentration Reactor H₂/C₂ C₆/C₂ (ppmv based Temperature molemole Residence on ethylene (° C.) ratio ratio time (hrs) feed) Example 1108 0.15 0.036 2.3 25.00  (Carbon Dioxide) Example 2 108 0.15 0.036 2.30.20 (Carbon Monoxide) Example 3 108 0.15 0.036 2.3 0.51 (CarbonMonoxide) Example 4 108 0.15 0.036 2.3 0.69 (2,4-hexadiene) Example 5108 0.15 0.036 2.3 2.78 (2,4-hexadiene)

For Comparative Examples A-B and for Examples 1-5: polymer flow indexwas determined based on ASTM D1238-F run at 190° C., with 21.6 kg weighthaving the standard designation for that measurement of 190/21.60;fluidized bulk density in the reactor was determined by measuring adifference in pressure across a known height of the fluidized bed;density was determined in accordance with ASTM D-792; catalystproductivity was determined by ICPES (Inductively Coupled PlasmaEmission Spectroscopy based on the chromium in the catalyst and thechromium in the polymer particles; and average particle size wasdetermined by a GRADEX™ G203-SP1. The results are shown in Table 3 andTable 4, respectively.

TABLE 3 Polymer Fluidized Average Flow Bulk Catalyst particle IndexDensity Density productivity size (dg/min) (kg/m³) (g/cm³) (kg/kg) (mm)Comparative 7.50 252 0.9475 9639 0.97 Example A Comparative 7.51 2560.9471 9257 0.94 Example B

TABLE 4 Polymer Fluidized Average Flow Bulk Catalyst particle IndexDensity Density productivity size (dg/min) (kg/m³) (g/cm³) (kg/kg) (mm)Example 1 5.16 260 0.9444 7857 1.02 Example 2 6.88 266 0.9453 3962 1.00Example 3 6.51 270 0.9447 3596 0.82 Example 4 11.0 228 0.9491 8738 0.89Example 5 8.80 242 0.9475 7664 0.98

The data in Tables 3 and 4 show that utilizing an active amount of theflow index modifier with the chromium catalyst modifies the polymer flowindex of the polymer being formed. For instance, utilizing an activeamount of carbon dioxide for Example 1 decreased the polymer flow indexby approximately 30%, as compared to Comparative Example A andComparative Example B; utilizing an active amount of carbon monoxide forExample 2 and Example 3 decreased the polymer flow index byapproximately 8% and 13%, as compared to Comparative Example A; andutilizing an active amount of 2,4-hexadiene for Example 4 and Example 5respectively increased the polymer flow index by approximately 47% and17%, as compared to Comparative Example A. Further, FIG. 2 for carbondioxide, FIG. 4 for carbon monoxide, and FIG. 6 for 2,4-hexadiene,respectively illustrate that utilizing an active amount of the flowindex modifier with the chromium catalyst modifies the polymer flowindex of the polymer being formed. FIGS. 2 and 4 illustrate that thepolymer flow index is decreased for utilizing an active amount of carbondioxide and carbon monoxide, respectively. FIG. 6 further illustratesthat utilizing an active amount of 2,4-hexadiene, the polymer flow indexvalues can pass through a maximum value located near the concentrationof 2,4-hexadiene of Example 4, and that increasing the 2,4-hexadieneconcentration therefrom, e.g., to the active amount of 2,4-hexadiene ofExample 5, can cause the polymer flow index to decrease relative to itshighest level at the maximum value observed.

Additionally, the data in Tables 3 and 4 show that utilizing an activeamount of the flow index modifier with the chromium catalyst modifiesthe density of the polymer being formed. For instance, utilizing anactive amount of carbon dioxide for Example 1 decreased the density byapproximately 0.003.1 g/cm³ as compared to Comparative Example A and0.0027 g/cm³ as compared to Comparative Example B; utilizing an activeamount of carbon monoxide for Example 2 and Example 3 respectivelydecreased the density by approximately 0.0022 g/cm³ and 0.0028 g/cm³ ascompared to Comparative Example A; and utilizing an active amount of2,4-hexadiene for Example 4 and Example 5 respectively increased thedensity by approximately 0.0016 g/cm³ and 0.0004 g/cm³, as compared toComparative Example A. Further, FIG. 3 for carbon dioxide, FIG. 5 forcarbon monoxide, and FIG. 7 for 2,4-hexadiene, respectively illustratethat utilizing an active amount of the flow index modifier with thechromium catalyst modifies the density of the polymer being formed.FIGS. 3 and 5 illustrate that the polymer density is decreased forutilizing an active amount of carbon dioxide and carbon monoxide. FIG. 7further illustrates that utilizing an active amount of 2,4-hexadienemodifier, the density can pass through a maximum value located near theconcentration of 2,4-hexadiene of Example 4, and that increasing the2,4-hexadiene concentration therefrom, e.g., to the active amount of2,4-hexadiene of Example 5, can cause the polymer density to decreaserelative to its highest level at the maximum value observed.

Additionally, the data in Tables 3 and 4 show that utilizing an activeamount of the flow index modifier with the chromium catalyst modifiesthe fluidized bulk density of the polymer being formed. For instance,utilizing an active amount of carbon dioxide for Example 1 increased thefluidized bulk density by 3%, as compared to Comparative Example B;utilizing an active amount of carbon monoxide for Example 2 and Example3 respectively increased the fluidized bulk density by approximately5.5% and 6.7%, as compared to Comparative Example A; and utilizing anactive amount of 2,4-hexadiene for Example 4 and Example 5 respectivelydecreased the fluidized bulk density by approximately 10% and 4%, ascompared to Comparative Example A. Further, FIG. 3 for carbon dioxide,FIG. 5 for carbon monoxide, and FIG. 7 for 2,4-hexadiene, respectivelyillustrate that utilizing an active amount of the flow index modifierwith the chromium catalyst modifies the fluidized bulk density of thepolymer being formed. FIGS. 3 and 5 illustrate that the fluidized bulkdensity is increased for carbon dioxide and carbon monoxide. FIG. 7further illustrates that for 2,4-hexadiene, the fluidized bulk densitycan pass through a minimum value located near the concentration of2,4-hexadiene of Example 4, and that increasing the 2,4-hexadieneconcentration therefrom, e.g., to the active amount of 2,4-hexadiene ofExample 5, can cause causes the polymer fluidized bulk density toincrease relative to its lowest level at the minimum value observed.

Additionally, FIG. 2 for carbon dioxide, FIG. 4 for carbon monoxide, andFIG. 6 for,4-hexadiene, respectively illustrate that utilizing an activeamount of the flow index modifier with the chromium catalyst can reducethe catalyst productivity, i.e., productivity kg/kg.

What is claimed:
 1. A method for modifying a polymer flow index,comprising: providing monomers to a polymerization reactor; providing achromium catalyst to the polymerization reactor; and providing an activeamount of a flow index modifier to the polymerization reactor, whereinthe flow index modifier is carbon monoxide and is from 0.010 parts permillion to 2.000 parts per million based upon the monomers, whereinproviding the active amount of the flow index modifier to thepolymerization reactor forms a polymer having a polymer flow index thatis reduced as compared to a second polymer having a different polymerflow index, where the second polymer is formed by a same polymerizationprocess, but without utilizing an active amount of the flow indexmodifier.
 2. The method of claim 1, wherein, the polymer flow index isreduced from about 5% to about 50% as compared to the second polymer. 3.The method of claim 1, wherein the monomers comprise ethylene.
 4. Themethod of claim 1, comprising forming polyethylene.
 5. The method ofclaim 1, wherein the chromium catalyst is a reduced chromium oxidecatalyst.
 6. A method for modifying a polymer flow index, comprising:providing monomers to a polymerization reactor; providing a chromiumcatalyst to the polymerization reactor; and providing an active amountof a flow index modifier to the polymerization reactor, wherein the flowindex modifier is 2,4-hexadiene and is from 0.05 parts per million to5.00 parts per million based upon the monomers.
 7. The method of claim6, wherein, providing the active amount of the flow index modifier tothe polymerization reactor forms a polymer having a polymer flow indexthat increased as compared to a second polymer having a differentpolymer flow index, where the second polymer is formed by a samepolymerization process, but without utilizing an active amount of theflow index modifier.
 8. The method of claim 7, wherein, the polymer flowindex is increased from about 50% to about 250% as compared to thesecond polymer.
 9. The method of claim 8, wherein, the polymer flowindex has a maximum value relative to a first active amount and a secondactive amount of the 2,4-hexadiene.